SAO PAULO: Brazil launched the World Cup with an emotion-fuelled 3-1 victory over Croatia on Thursday as an opening day which began with violent clashes gave way to an outpouring of joyful celebrations.

Barcelona superstar Neymar scored in each half as Brazil recovered from conceding an early Marcelo own goal to set up a win before hordes of golden-shirted fans at the 61,600 Corinthians Arena in Sao Paulo.

Chelsea midfielder Oscar put the seal on the win with a late strike from distance to trigger delirium.

The host nation's Group A victory was greeted by an explosion of fireworks across Sao Paulo, a sharp contrast to several hours earlier when riot police fired tear gas and stun grenades to disperse angry protests.

But a largely free-flowing tournament-opener was shrouded in controversy, with Brazil's second coming courtesy of a dubious penalty when Croatia defender Dejan Lovren was harshly adjudged to have shoved Fred over.

The hosts, chasing a record sixth World Cup, had also enjoyed a degree of good fortune in the first half when Neymar received only a yellow card for elbowing Croatia's playmaker Luka Modric.

Moments later Neymar scored Brazil's equaliser to settle home nerves after Marcelo's 11th-minute own goal.

Lovren was furious with the performance of Japanese referee Yuichi Nishimura, branding his display a “scandal. “ “Two billion people I think saw that it was not a penalty. I didn't touch him,” Lovren said.

“It wasn't a mistake, it was a scandal. “

National pride

Pop superstars Jennifer Lopez and Pitbull headlined a lavish opening ceremony which included the appearance of a paraplegic wearing a robotic bodysuit controlled by brain signals who performed a ceremonial kick-off.

The match began after a hearty rendition of Brazil's national anthem with fans — exhorted to unite behind the team by coach Luiz Felipe Scolari — roaring their support for the “Selecao". Even after the music stopped, fans and players belted out one more verse.

Brazil captain Thiago Silva epitomised the mood, bellowing a rallying cry to his team-mates as they embarked on their quest to earn a first title on home soil.

The victory provided a euphoric counterpoint to scenes earlier in the day when violent protests in Sao Paulo had threatened a stormy start to the month-long football extravaganza.

It had been a torrid seven-year build-up bedevilled by delays and public anger at the tournament's $11 billion cost, and scattered protests took place Thursday in several of the cities which will host World Cup games.

The worst violence took place just a few kilometres from the opening match, as anarchist demonstrators in black shirts and masks lit bonfires of rubbish after armoured police sought to quell protests.

But Sao Paulo and other cities largely went quiet as the game started.

Yellow and green flags hung from many buildings.